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Therefore, a large number of methods have been explored in recent years, in order to obtain higher strength and toughness of the magnesium alloy.
It can be seen that the microstructures are the equiaxed grains with the average grain size of 3.4μm, but the average grain size of AZ31 alloy prepared by the same process is 5.6μm [4].
When the dislocation pile up to a certain extent will rearrange and combine, producing dislocation cells and sub-boundaries, sub-boundaries further transforms into high angle grain boundary, and ultimately into the recrystallized grains with high angle grain boundaries.
Although the grains slightly grow up along the stretching direction, but still are equiaxed grains, which indicates that the grains growth and movements that along the grain boundaries are isotropic and GBS is the main deformation mechanism of AZ31+Sr+Y alloy during the superplastic deformation process.
When temperature increases to 400℃, the fracture morphology exhibits a large number of dimples and tear ridge which connecting dimples (as shown in Fig. 7d), proving that the fracture mode changes from microviod accumulation fracture to intergranular fracture.

While most grains are of the order of only 3 µm, larger grains of 10 to 12 µm in size are also present.
The arrow in Fig. 3a points to a high angle grain boundary which is incomplete and has "degenerated" into low angle grain boundary tails.
The grains are almost equiaxed and the variation in grain size is significantly reduced.
As the number of ECAP passes increases from 2 to 4 (Fig. 5c), the intensity of this texture component is clearly becoming more dominant.
As the number of ECAP passes is increased from 2 to 4, both yield stress and tensile strength are enhanced.

SEM experiment conforms that the average grain size of sintered body is less than 300nm.
A number of researchers have demonstrated superplasticity in several silicon nitride ceramics by applying the transient liquid phase[3,4], using ultrafine β-phase powders[5,6], or by adding secondary phases into Si3N4 to refine the microstructure[7].
Microstructures of as-hot-pressed materials are very fine and uniform, with average grain sizes about 300nm.
Alternatively, at constant stain-rate, the forming temperature can be decreased with smaller grain size.
Microstructures of as-hot-pressed materials are very fine and uniform, with average grain sizes about 300nm.

In order to investigate effects of a grain size of the source diamond, EDM cutting experiments were conducted on the EC-PCD specimens of 4 different grain sizes.
In the case of S-PCD, the cutting speed for the 25µm grain size was lower by 15% or so compared with the10µm grain size.
In both cases of 10µm and 25µm grain sizes, surface roughness value of the EC-PCD was smaller than that of the S-PCD by 40% or so, and the EC-PCD of 25µm grain size after EDM cut showed the surface roughness identical to the case of the S-PCD of 10µm grain size.
In the SEM image of the S-PCD surfaces, a number of the pits created by preferential removal of the cobalt can be observed.
This phenomenon becomes prominent as the diamond grain size gets larger.

The different conditions of finishing stage of TMCP adopted here are described as follows, respectively with respect to start strip thickness and number of passes applied during finishing stage: - #0: no formal holding stage; - #1: 30 mm; one pass; - #2: 30 mm; two passes; - #3: 50 mm; three passes.
The comparison of these micrographs suggests that grain size of the #0 is the finest.
It can be seen that the contribution of grain size is predominant.
As expected, higher holding thicknesses and number of passes during finishing rolling increased total rolling time and decreased the productivity of the Steckel Mill Line.
Gladman, Grain-Refined C-Mn Steels, Journal of the Iron and Steel Institute, February 1967, 161-182

Lots of the fine grain is formed.
Between them there are some regions composed by coarse grains and fine grains.
A lager number of needle-like γ precipitates disperses in the deformed grains under high magnification image (Fig. 2).
When extrusion ratio reaches to 17, the average grain size of the alloy arise again due to the R-grains coarsening.
In few parts of the deformed grains are extruded to a critical level to form a minute quantity of small grains.

The grain structure exhibits in this case bands and also large pancake like grains in the center as well as at ¼ of the thickness.
According to the complexity of the microstructure across the thickness the grain structure have been characterized by the parameter T = L / N for the bands, L is the length of a band and N gives the number of grain boundaries intercepted.
For more or less equiaxed grains a mean grain size d was determined by linear intercept method.
We see finally bands, pancake like grains, and in the surface region small grains.
One obtains grain growth in the surface region.

Therefore, many research focused on the size effect in metla forming of mini parts and it can be characterized by volume grain size, surface grain size and grain size to thickness size effect [3].
Material and methods The spur gear specifications are shown in Table 1, In order to evaluate the effect of annealing treatment on grain size resulting in varying deformability of the commercial pure titanium (grade 2, CP2), a mini gear with an outside diameter (2*R0) of 9.2 mm, number of teeth (N = 8), and face width (h) of 5 mm, was proposed as shown in Fig. 1.
Specification of spur gear dies Parameters Value Number of teeth 8 Module 0.92 Pressure angle(˚) 20 Pitch diameter (mm) 7.36 Addendum circle (mm) 9.2 Dedendum circle (mm) 5.06 Face width (mm) 5 Modification coefficient 0 Fig. 1.
Fig. 3 (c) reveals that grain forms when AT is 700°C and the average α-phase grain size is 96.7µm.
Therefore, the average grain size for the specimen that contains β-phase grain is not calculated.

Depending on the applications, a number of different steel grades, coupled with proper process routes, can be used.
The focus is mainly placed on the role of prior austenite grain size (PAGS).
In the case of MC-B steel, repeated cycles resulted to be useful to reach the fine grain condition.
This result is not surprising because the model, which takes into account recrystallization and grain coarsening, considers very low interpass time and high strain rates (typical of wire rod rolling), which allow for a higher grain refinement.
Yield strength, which is affected by ferrite grain size, increases with PAGS refining, and yield point elongation (YPE) is clearly more pronounced when grain size gets smaller (Fig. 5).

By controlling the number and size of large particles, the nucleation sites for recrystallization can be controlled and by controlling the number of dispersoids and elements in solid solution, the nucleation and growth can be decelerated.
This will in turn lead to dissolution of the dispersoids close to the grain boundaries.
In the smallest grains (given by the sample-section) no dispersoids were found and in the larger grains the dispersoid size and number density varied with the position in the grain.
In addition, a small number of Si-particles were found in this alloy.
To further investigate this, the number density of dispersoids was measured in the TEM in samples heated to 500 o C and then quenched.